Simplify topology to 3 agents + 2 tools

Harden Gemini structured-decoding contract and write_memory semantics

Switch to Gemini 3.x latest aliases; grounded WebSearch; lab results in UI

Phase 4: Close RCE in ComputationTool + guardrails (PII, prompt injection, HITL)

Phase 1: Pydantic schemas + Gemini response_schema (constrained decoding)

Initial commit: existing Nutrition MAS prototype